The present invention relates in general to spark-ignited gaseous fuel engine technology and a sealing accessory for the ignition coil and valve cover interface. More specifically the present invention relates to the use of a grommet to seal the ignition coil-to-valve cover interface as well as sealing the area between the ignition coil and a spark plug adapter tube. In a related embodiment of the present invention, the grommet is designed with a unique vented design to safely release the internal air pressure which builds up in the spark plug adapter tube during engine operation.
Current engine technology, such as that associated with large, stationary gaseous fuel four-valve engines, may incorporate an ignition system which is typically described as a coil-on-plug or COP ignition system. In this type of engine and ignition system, as is believed to be well known to those of ordinary skill in the art, there is a spark plug, a spark plug adapter tube, an ignition coil, and a valve cover. FIG. 1 herein provides a cross sectional illustration of this ignition system and the primary components, all of which are believed to be known to one of ordinary skill in the art. In the interior space beneath the valve cover and around the spark plug adapter tube, there is lubricating oil which is jetted and splashed around during engine operation due to overhead lubrication. It is possible for this lubricating oil to flow or leak through the space between the spark plug adapter tube and the valve cover. If this occurs, it is possible for the oil to then back flow into the spark plug tube bore where it can cause ignition misfire and other service problems.
It may have been contemplated in the past to wedge an O-ring between the valve cover and the spark plug adapter tube in order to block the flow or leakage of oil, but this creates its own problems. Another option might have been the use of a flat face seal on the coil, but this also generates certain problems. For example, once the ignition coil is removed, there is nothing on the valve cover to use to pull on or leverage in order to remove the cover. With the cover and the tube in effect anchored together due to the wedged O-ring, removal of the cover is made quite difficult. Removal of the valve cover would be required periodically in order to adjust valve lash. Accordingly, this becomes an efficiency and an ease of servicing issue as well as a sealing issue. It is desired to prevent the flow of oil into critical operating areas and whatever style of O-ring or grommet may be used, it needs to be an effective liquid sealer. If there is no sealed interface once the coil is removed, then the various components are not, in effect, locked together by having a seal or an O-ring wedged between them. It would therefore be an improvement to the O-ring designs which may have been tried by others to find a way to eliminate any O-rings without sacrificing the desired sealing between the spark plug adapter tube and the valve cover and, if needed, the sealing between the ignition coil and the spark plug adapter tube.
There is a further concern to be addressed with virtually any type of sealing/O-ring arrangement for this engine application, even with the present invention, and this concerns the air pressure build up on the interior of the spark plug adapter tube due to the fixed volume of air which is trapped therein. This fixed volume of air is subjected to an elevated temperature during engine operation and accordingly the air is heated at a constant volume, generating a higher pressure. The tube interior volume is a sealed volume once the seals are installed for the prevention of oil leakage. Accordingly, there is initially a fixed mass of air inside the tube which is heated as the interior temperature rises. This heating of the fixed volume of air causes the interior air pressure to increase. Since large, stationary gaseous fuel engines of the type being discussed herein are typically serviced while still warm or hot, with only a brief cool down period, there is still an elevated interior pressure as the service technician begins working on the engine. As engine components are disassembled for servicing, specifically the ignition coil, there is a risk that the components used for sealing in order to prevent oil leakage will act like a cork on a champagne bottle. As the "cork" is dislodged, a loud "pop" sound is heard and this can be very unnerving to the service technician.
Engines of the type being discussed herein are relatively large and a step ladder or some type of elevated platform is normally used by the service technician in order to climb up and get in position. The loud "pop" sound comes as a shock to the service technician and there is a concern that this individual may be distracted and lose his balance on the step ladder. The built-up pressure in the tube may also be large enough to partially eject the coil, like the cork on a bottle, and this presents another concern. If the interior pressure could be relieved or gradually vented in some fashion before any components are disassembled, then the loud "pop" sound would be prevented and there would not be the same level of risk of components, such as the ignition coil, being partially ejected.
The present invention provides two improvements to the foregoing design problems and concerns. The first improvement relates to a way to eliminate any O-ring seals as previously discussed. The second improvement relates to a way to provide gradual venting of the interior volume. While each of these improvements are novel and unobvious individually, the present invention also contemplates the integration of both improvements into a single unitary component.